This invention relates generally to a filtering device adapted to be used with a syringe and a needle; and, in another embodiment of the invention, to a combination syringe, needle and filter.
The current state of the art of syringe filters is believed to involve the use of a round flat sheet microporous membrane that is sealed between two plastic halves as an intermediate filter typically for use between a syringe and needle. If air is introduced to the syringe side of one of these filters and pressure is applied, the air is compressed over the entire surface area of the membrane thus substantially blocking or minimizing the flow of fluid. It will be appreciated, that if liquid is introduced to the syringe side of the flat filter (which is horizontal to the vertical axis of the syringe and needle), the liquid will only cover the entire surface of the membrane, in most cases, if the syringe and needle are in a vertical position. If the syringe and needle are in a horizontal position, or angled, the liquid may only cover part of the surface of the membrane thus causing air blockage. Moreover, increased filtering capacity of such filters can only be attained by increasing the diameter resulting in filters having dimensions that sometimes exceed the diameters of the syringe barrels to which they are attached and result in awkward handling.
In recent years, attempts to devise various syringe filters have resulted in that shown in U.S. Pat. No. 4,316,462 which discloses an adapter which extends between the needle that is already in place on the syringe and a second needle. A flat membrane filter is used in this adapter.
According to this invention, there is provided a filtering device adapted to be used with a syringe and a needle wherein longitudinally positioned hollow filter fibres and a flow blocking material are arranged within the tubular body for directing flow through the material of the hollow fibres. The device according to the invention can be embodied either as a single filter element or as a combination syringe, filter and needle.
The foregoing arrangement produces the advantage that, even though the syringe and needle are tipped from vertical during use, the fluid will pass through the filter fibers tangentially to the longitudinal axis of the filter, thus eliminating air blockage. If air is present, any air blockage that will occur will be minimal compared to the flat membrane filters.